feat(backend): initial setup and auth routes (#8)

## Description
Adds an axum powered backend with swagger + authentication using PASETO
tokens

## Related Issue
Closes #4, #3, #2 and #1

## Proposed Changes
* Adds a rust backend using:
  * `diesel` for database
  * `axum` for web server
  * `utoipa` for documentation

## Testing Done
Tested in the swagger ui

## Checklist
- [x] I have tested my changes locally and they work as expected.
- [ ] I have documented any new or modified functionality in the project
documentation.
- [x] I have added appropriate comments to the code, especially in
complex or non-obvious sections.